1. Field of the Invention
The present invention is directed to the field of alternator rectifier bridge assemblies and more particular to that portion of the above-noted field which is concerned with the manufacture of rectifier structures which structures may be conveniently received with an alternator housing and which structures are useful in converting poly-phase AC alternator output to a DC potential for application to a vehicle electrical system which may include, for example, a storage battery. More particularly still, the present invention is concerned with that portion of the above-noted field which is directed to the manufacture of alternator rectifier bridge assemblies in which the DC terminals also act as heat sinking means to maintain operating temperatures below those temperatures at which semi-conductor rectifier elements are destroyed. More particularly still, the present invention is concerned with the method by which alternator rectifier bridge assemblies may be conveniently fabricated on automated equipment, making use of a commercially available rugged forms of semi-conductor diode elements, and which require only a single exposure to an elevated temperature to solder all electrical connections.
2. Description of the Prior Art
The prior art teaches that a poly-phase AC alternator output may be rectified to a DC potential by connecting pairs of diodes in electrical series relationship with the common anode/cathode electrode of each diode pair connected to receive one phase of the poly-phase output of the alternator. The other anode and the other cathode of each diode pair will comprise at least a portion of each of the DC terminals. Three such pairs of diodes, each having their common anode/cathode electrode connected to one phase of a three phase alternator output, may be connected in parallel to provide full wave rectification for the three phase alternator and will provide the DC potential between their common anodes and their common cathodes.
The applicant's pending application Ser. No. 379,136, "Semi-Conductor Rectifier Heat Sink Assembly" described a rectifier assembly and illustrates one form by which such devices may be assembled. As there illustrated, canister type semi-conductor diode devices are received within heat sink structure. Each diode device has an extending electrical lead, which may comprise either the anode or the cathode electrode, which lead is communicated to a circuit board member where it is soldered to a portion of the electrical circuit therein provided. As illustrated in the noted application, the rectifier bridge assembly is generally U-shaped and may be conveniently mounted within one end of the alternator structure with the axis of the alternator rotor extending through the U. This provides a relatively simple packaging arrangement for those who desire to use such structures. However, the use of canister type diodes results in certain handling problems stemming from the frailness of such devices. The insertion of the extending electrode wires through the circuit board member frequently requires a hand operation to align the projecting leads with holes provided therefor in the circuit board. It is therefore an object of the present invention to provide an alternator rectifier assembly which is generally U-shaped in configuration and which is mechanically sturdy and rugged. Since the frailness of the prior art devices resulted in part from the configuration of the diode devices, i.e., diode devices having extending electrode leads, it is a further object of the present invention to provide an alternator rectifier assembly which utilizes diode devices which are free of any extending electrode leads. It is a further object of the present invention to provide such a device wherein the circuit board member and the DC terminal plate members (heat sinks) are in mutually supporting contact.
U.S. Pat. No. 3,648,121 issued to M. Suenaga et al. describes a structure which generally achieve the aforementioned objectives. Therein a generally U-shaped alternator rectifier bridge assembly having integral heat sink structure is shown to be fabricated into a composite body with the circuit board member in physical contact with the DC terminal plate members (heat sinks) over an extended surface area. This provides for an increased strength in the device without any substantial loss in the heat sinking capability of the heat sink member. This structure also avoids the necessity for accurate positioning of the holes of a circuit board member in registry with the extending electrode leads of the canister type diode devices.
The Suenaga et al. reference teaches the use of the heat sink members as the base layer with successive layers of material, termed therein "prepreg", overlaying the base layer. The prepreg material is, for example, an epoxy resin impregnated fibrous material such as fiberglass fabric and includes a plurality of voids or recesses. A plurality of semi-conductor rectifier wafers are positioned within the voids and an overlaying layer of conductor strips is arranged to interconnect selected diode pairs. Solder material is also provided in preforms where necessary. This composite is thereafter passed through several heating ovens in order to flow the solder to establish the electrical connections and to cause the resinous material in the prepreg to flow and bond the structure into a unitary composite. This material will also flow into the diode recesses to support and insulate the diode wafers. While the resulting rectifier bridge assembly is of great utility and possesses the desired ruggedness in handling, the requirement that the materials withstand several passages through heating ovens operating at different temperatures results in a greatly increased risk of semi-conductor failure because of the temperature involved. Additionally some failures have resulted from an uneven flow of the resinous material which produced bubbles and weak spots within the composite assembly. It has also been observed that the resulting rectifier bridges are relatively delicate in that the cured epoxy or resinous material and the layered materials enclosed therein are subject to fracturing if mishandled prior to assembly within an alternator. This fracturing results from the extreme hardness and brittleness of the epoxy and may occur when a rectifier assembly is dropped or when adjacent rectifier assemblies forcibly contact each other during packaging, shipping or other incidental handling. These fractures greatly weaken the mechanical strength of the rectifier assembly and also constitute a source of potential electrical failure since the conductors may be exposed to contamination. It is therefore an object of the present invention to provide an alternator rectifier assembly which is rugged and which has a relatively resilient circuit enclosure.
It is therefore a further and specific object of the present invention to provide an alternator rectifier bridge assembly which does not require the application of heat at differing temperatures in order to accomplish bonding. It is a further object of the present invention to provide a rugged alternator rectifier bridge assembly wherein the circuit board member and the DC terminal plate members are in close physical contact and which utilizes diode elements which are adequately insulated without requiring that resinous material flow about the semi-conductive rectifier wafer. It is also an object of the present invention to provide a method of assembly of an alternator rectifier which method will result in a unitary composite rectifier/heat sink structure which method does not require the application of heat or thermal energy other than that necessary to flow the solder material to provide electrical connections. It is also an object of the present invention to provide such a rectifier bridge assembly having a generally U-shaped configuration which may be conveniently assembled to an alternator structure by mounting within the housing thereof. It is also an object of the present invention to provide a method of assemblying an alternator rectifier in which the DC terminal heat sink members may be fixedly attached to, and in close physical contact with, a circuit board member formed of a plastic material having the circuit elements embedded therein. More particularly still, it is a specific object of the present invention to provide a method of assembly for an alternator rectifier assembly comprised of heat sink members and circuit board member which are held in assembled relationship by the means of rivets.